1. Field
The present disclosure relates to wireless network technology, and more particularly, to technology for setting a frequency band to be scanned in a wireless local area network (WLAN) in which a plurality of frequency bands are used.
2. Discussion of Related Art
Recently, a demand for mobile devices has been drastically increased. Mobile devices communicate radio signals with access points (APs) that provide access to a wireless network through defined frequency channels. A typical example of such a wireless network that provides a service for a mobile device is a WLAN, which is widely used for business purposes, public facility-related purposes, personal purposes, and so on. The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard for a WLAN mainly covers a physical layer and a media access control (MAC) layer.
A WLAN system includes one or more basic service sets (BSSs). A BSS is a set of stations that can be synchronized to communicate with one another. In a broad sense, the stations include AP stations and non-AP stations. For the sake of convenience, however, an AP station may be simply referred to as an AP and a non-AP station as a station. Meanwhile, a non-AP station may also be referred to as a mobile station (MS), a mobile terminal, user equipment (UE), or the like.
FIG. 1 schematically shows an exemplary configuration of a WLAN.
As shown in FIG. 1, stations 152 and 154 may access a WLAN 100 via APs 111, 113, 115, 117, 121, 123, and 125. For example, the access to the WLAN 100 may be performed according to a protocol of the IEEE 802.11 standard. Such a WLAN 100 as mentioned above is referred to as an infrastructure network. In the WLAN 100, each of the APs 111, 113, 115, 117, 121, 123, and 125 manages the station(s) 152 and/or 154 associated with itself as one or more entities constituting a BSS. The APs 111, 113, 115, 117, 121, 123, and 125 are identified by basic service set identifiers (BSSIDs).
The exemplary WLAN 100 includes a distribution system (DS) that interconnects the plurality of APs 111, 113, 115, 117, 121, 123, and 125 and provides an extended service set (ESS), although it is not shown in FIG. 1. As a mechanism for one AP to communicate with another AP, such a DS enables an AP to transmit a frame to stations connected to a BSS managed by the AP, deliver a frame to a station that has moved to another BSS, or deliver a frame over an external network such as a wired network. As such, APs and stations included in one ESS may communicate with one another. In other words, a single ESS may be considered as a single logic network segment present in one Internet protocol (IP) subnet. Such an ESS is identified by a service set identifier (SSID). As shown in FIG. 1, the SSID “mobile” is an identifier indicating the WLAN 100 and is transmitted from the APs 111, 113, 115, 117, 121, 123, and 125 as information indicating the presence of the WLAN 100. According to the IEEE 802.11 standard, an SSID may be signaled using a management frame named a beacon frame or another one named a probe response frame.
Under such a scenario, the stations 152 and 154 may roam between the different APs 111, 113, 115, 117, 121, 123, and 125 having the same SSID. In other words, in the WLAN 100 (SSID: mobile), the stations 152 and 154 may move from one BSS to another BSS through roaming. For example, when the station 152 connected to the AP 113 moves and a communication signal from the AP 113 is attenuated, the station 152 attempts to connect to another AP (e.g., the AP 115) to change its connection point before the connection to the AP 113 is completely lost. In a preparatory process for such roaming, the station 152 scans frequency bands (e.g., the 2.4 GHz frequency band and the 5 GHz frequency band) used for wireless connections in the WLAN 100 to search for an AP that sends a signal at a satisfactory level. The scanning may follow either an active scanning mode or a passive scanning mode. According to the active scanning mode, the stations 152 and 154 transmit probe request frames and then wait for probe response frames. According to the passive scanning mode, the stations 152 and 154 wait for beacon frames from the APs 111, 113, 115, 117, 121, 123, and 125. For example, the station 152 discovers the AP 115 from which a beacon frame or a probe response frame is received at a higher strength, selects the AP 115 as an AP to which a new connection is to be made, and sends a reassociation request frame to the AP 115.
It is of primary importance to improve the communication performance of a mobile device in a wireless network (e.g., WLAN) for providing a service to the mobile device. Particularly, for an application such as voice over IP (VoIP) or video conference that actually requires real-time delivery of voice/image traffic, it is necessary to maintain such a traffic flow in a stable manner. In addition, it is preferable to prevent degradation of the communication performance caused by radio interference in some frequency band for use in wireless connections in the wireless network.